Field of the Invention
The present invention relates to an apparatus for reading an image formed on a sheet fed from a sheet feeder.
Description of the Related Art
The density of an image that an electrophotographic type image forming apparatus forms on a sheet fluctuates in accordance with various factors. For example, when environmental conditions such as the temperature or humidity change or when a part of an image forming apparatus changes over time, the density of an image formed by the image forming apparatus also changes. Accordingly, the image forming apparatus performs a calibration for controlling the density of an image to a target density. In the calibration, an image density is obtained by forming a test pattern on a sheet and reading it by a sensor, and parameters are corrected in order to adjust the image density so that the image density becomes the target density. Note that parameters for adjusting the image density are controlled by parameters that correspond to the type of a sheet (grammage, the existence or absence of a coating, whether it is recycled paper, and so on). Here, an image forming apparatus recited in Japanese Patent Laid-Open No. 2007-329929 reduces an operational burden for a calibration by using an automatic document feeder (ADF) to cause a test chart to be conveyed, in order to read the test chart.
Incidentally, from sheets onto which an image can be formed by an image forming apparatus, there are sheets that are difficult to convey by an ADF (for example, thick paper, coated paper, and recycled paper). When causing such a sheet to be conveyed by an ADF, there is a possibility for a jam to occur. However, calibration is necessary even for such a sheet.